Control of a compacting machine

ABSTRACT

A roller machine for compacting is provided with control devices for varying the oscillation movement of the body. The movement of the body may be affected by a weight attached thereto. The oscillation of the vibration body is measured. From this measurement, the portion of the oscillation is determined having a frequency corresponding to half the excitation frequency and the portion for other oscillation, in particular the excitation frequency, are also determined. The excitation of the vibrating body is controlled so that the harmonic component having half the excitation frequency will be in a predetermined proportion of the component of the oscillation component. Such control avoids undesired oscillation movement.

FIELD OF THE INVENTION

The present invention is related to control of a vibrating compactingroller and similar devices for compacting or compressing a more or lessdense material such as ground surfaces of the types earth or soil, roadembankments, asphalt, etc, the term "ground" meaning a surface to becompacted, located underneath the compactor.

BACKGROUND OF THE INVENTION AND PRIOR ART

In compacting a ground material it is naturally desirable to have itperformed as rapidly and as efficiently as possible. For a vibratingroller machine or another vibrating body contacting the ground differentparameters may be varied for this purpose, in many cases most simply inthe excitation imparting the vibrating movement to the roller. It isthus possible e.g. to increase the amplitude of the vibration by meansof different devices coupled to an eccentrically arranged weight whichin the common way produces the vibrating movement. Such a loaded andvibrating roller of a compacting roller machine can, in a hard operationwith a large vibratory movement, enter undesired oscillating states suchas double jumps (the roller is in contact with the ground only at everyother stroke of the eccentric mass) and cradle oscillation (the axis ofthe roller is swung about swinging axis perpendicular to the rolleraxis, so that a hard blow or jolt is obtained in the area at one end ofthe roller only at every other stroke of the exciting, eccentricallyarranged weight, and in the other strokes a hard blow or jolt isobtained in the area at the other end of the roller). In these undesiredoscillating states even a disintegration of the ground material may takeplace.

There is thus a need of methods and devices for allowing the operationof e.g. a roller machine with an oscillating movement which is as largeas possible, avoiding that the roller enters the undesired oscillatingstates mentioned above.

From the Swedish patent 8202103-1 for Dynapac Maskin AB (corresponds toU.S. Pat. No. 4,546,425 and DE-A1 33 08 436) it is previously known tocontrol a vibrating roller machine so that the amplitude of thevibratory oscillations of the roller machine is increased continuouslywith a predetermined velocity, as long as the vibration movement of theroller machine is regular or as long as the irregularity of thevibration movement does not exceed selected amplitude values. In thispatent it is not described, however, how the irregularity can be or isto be measured and evaluated. Signal sensors mounted to the roller orthe frame of the roller generate signals and the difference of thesesignals or the deviation of these signals from a harmonic oscillatingshape is fed to an amplitude adjusting device of an eccentric elementexciting the vibratory movement of the roller drum. The continuous,smooth increase of the amplitude is interrupted when this difference orthis deviation achieves some predetermined values. Then the excitingeffect of the eccentric element is reduced so that the amplitude of thevibratory movement will continuously decrease somewhat, with apredetermined smooth velocity during a given time period, after whichthe excitation degree is increased again, so that the amplitude of thevibrating oscillations of the roller drum again will increasecontinuously, after which the procedure is repeated. In this patent itis not mentioned, as has already been indicated, anything on the matterhow the regularity or the irregularity of the vibration movement of theroller can be measured or estimated.

Other methods for the control of a vibrating roller machine appear fromU.S. Pat. Nos. 3,797,954 and 4,330,738, DE patent document 25 54 013 andGB patent document 1,372,567. The measurement of the amplitude of thevibrating movement and the compaction degree achieved are treated inU.S. Pat. No. 4,103,554 and the international patent application havingpublication number WO 82/01905.

DESCRIPTION OF THE INVENTION

It is a purpose of the invention to provide a method and a device forthe control of a vibrating roller machine or another vibrating devicefor compacting and compressing a base or ground material such as earthor soil, by means of which the compaction of the material is performedwith an efficient use of controllable oscillating movement of avibrating compaction body.

It is another purpose of the invention to provide a method and a devicefor the control of a vibrating roller machine or similar device so thatthe excitation of the roller, in the compaction of the ground material,is made as strong as possible.

These purposes are achieved by the invention, the more close featuresand characteristics of which appear from the appended claims.

A roller machine or another device for compacting earth, soil or similarmaterials is provided with control devices for variation of theoscillating movement of the roller or the compacting body, this movementbeing excited by an eccentric body. The oscillation of the vibratingroller or the compacting body is measured and therefrom the oscillationportions are determined having a frequency corresponding to half theexcitation frequency, and for other oscillation modes and particularlycorresponding to the excitation frequency. The excitation of thevibration of the roller or compacting body is controlled, so that theportion of the oscillation component having half the frequency will be apredetermined portion of the component of the other oscillationcomponents or at least in such a way that this portion will be as closeas possible the desired value in regard of the possible excitation,bearing stresses and similar factors.

The oscillating movement of the roller or compacting body can becontrolled in various ways, both by varying the excitation, and bychanging other parameters such as the rotation velocity of the roller inthe rolling traversal movement thereof over the ground and the staticload or force which the roller or the compacting body respectivelyimparts to the ground material. In the latter case the mass distributionof the roller machine can be changed by displacing static load masses,e.g. by pumping water between different containers. In a variation ofthe excitation an excitation body may be given a stroke length having avarying size, for a rotational excitation an eccentric body can be givenan eccentricity of different sizes, the mass of the excitation mass orthe mass of the eccentric body can be changed and the frequency androtational velocity respectively of its vibrating movement can bechanged. In a standard case with one single type of variable excitationarranged in the machine excitation means may be arranged which in thecontrol of the excitation thereof are arranged to excite the compactingbody so that its resulting oscillating movement for varying excitationdegrees will have substantially varying amplitudes or substantiallyvarying frequencies.

In the measurement of the oscillating movement of the rolleradvantageously a sensor can be used which can be mounted to a frame partsuch as a bearing plate in which the roller is rotatably mounted. Thesensor can also be arranged directly on the compacting body. The sensoris then arranged to produce a signal which in some way represents theoscillatory movement of the roller or of the compacting body and inparticular the oscillating movement in an approximately verticaldirection. e.g. in a plane through the rotational axis of the rollerdeviating at most 30° from a vertical plane. The plane should furtherpass approximately symmetrically through the compacting body and for aroller thus through its rotational axis. Advantageously an accelerometeris used as a sensor, the output signal of which can be directly used asa measurement of the oscillating movement. Alternatively a sensor can beused directly generating signals representing the velocity ordisplacement of the roller or the compacting body. From an accelerationsignals also such signals can be determined by an integrating operationin an integrator but it produces no more information.

In an analogue circuit for producing a signal representing theoscillation portion or component having half the frequency the signalfrom the sensor, which can possibly be first processed for filteringaway too extreme frequencies, this filtering being performed byintegration or similar methods, is fed to two band-pass filters havingnarrow pass-bands centered around center frequencies whichadvantageously are adjustable or controllable. The center frequenciesare selected in such a way that one corresponds to half the frequency ofthe vibration frequency of the excitation of the roller and the othercorresponds to this excitation frequency. Signals representing theamplitude of the components, which have been filtered out, are thenproduced by rectifying and low-pass filtering. The amplitude signalsthus obtained are delivered to a division circuit which then producesthe desired signal on its output terminal.

For control of the center frequencies of the band-pass filters a pulsesignal having a suitably high frequency can be produced from the signalof the sensor, which signal is shaped into pulses and is fed to aphase-lock circuit containing a frequency division circuit. The pulsesignal thus produced is then fed to one of the band-pass filters whilethe other band-pass filter receives the corresponding pulse signal whichhas passed through a circuit for extracting pulses having half thefrequency imparted to the roller.

In a corresponding digital circuit the corresponding signal processingcan be performed in a central logic unit or processor. The signalrepresenting the oscillatory movement is converted in the common way,first by sampling in a converter to a digital shape to be fed to theprocessor. The sampling in the converter can be controlled concurrentlywith the periods of the oscillatory movement. Therefor, like theanalogue case, pulses are generated, representing the frequency of theoscillating movement, directly from the sensor signal. In other cases apulse sensor can be provided producing pulses representing the frequencyof the excitation and also representing a definite phase positionthereof. From this signal a signal is produced having pulses of a higherfrequency, this frequency being a predetermined, e.g. an even, multipleof the excitation frequency. When these signals having higherfrequencies are fed to the converter, it will during each oscillationperiod always produce the same number of sampled digital values. Itfacilitates the calculations in the processor. The signals having ahigher frequency for the control of the sampling will then also have acertain, fixed phase position in relation to the periodic excitation.

The mentioned control of the sampling times of the converter can be usedin the control of the vibratory movement of roller machines and othercompacting devices, whenever an evaluation or processing of theoscillation movement is desired in a digital shape, in order to be ableto influence the size and/or frequency of the vibrational movementsand/or to adjust the excitation parameters. Generally, in such a controlin some way the times are determined when each oscillation period stops.The time period between these times is divided into a predeterminednumber of equally long time periods or slots and the sampling isperformed in each such slot such as at the beginning thereof. The startof each oscillation period can be determined from the times when theoscillation signal passes some predetermined level in a predetermineddirection, possibly after some preshaping of the signal, e.g. when thesignal passes the zero level. Alternatively information is obtainedrelating to the beginning of the oscillation period from some othersignal, e.g. as obtained from a pulse sensor sensing the excitation. Thecontrol signals for the sampling will then like above be given adefinite phase position in relation to the periodic excitation which canbe valuable in the determination of control parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described as a not limiting embodiment withreference to the accompanying drawing in which

FIG. 1 is a block diagram of a control system of a roller machine,

FIGS. 2-3 are schematic pictures from the side which illustratedifferent ways of producing an oscillation movement of an earthcompacting roller,

FIG. 4 schematically shows the mounting of a sensor on a bearing plateadjacent to a compacting roller,

FIG. 5 shows signals determined by an accelerometer for different rollerexcitations,

FIG. 6 shows a block diagram of an analogue production of a controlsignal,

FIG. 7 shows a block diagram of a digital production of a controlsignal.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 the system is shown for control of a vibrating roller 1. Theroller 1 is provided with a weight 3, which is arranged therein, iseccentrically located and rotatable and which rotates about the samerotational axis 5 as the roller 1. The rotating weight 3 excites theroller 1, so that it performs an oscillatory or vibrational movement.The excitation can further be varied by influencing the rotationalvelocity of the body 3 and/or the size of its mass or its eccentricposition. The rotating weight can also, in the conventional way, bedivided into two part masses placed close to the ends of the shaft 5, sothat the exciting force can be transferred to the roller withoutsubjecting the rotating shaft to an unnecessarily large bending moment.

The vibratory movement of the roller is sensed by an accelerometer 7placed on one of the frame parts such as a bearing plate 9, in which theroller 1 is rotatably mounted, see FIG. 4. The bearing plate 9 isfurther resiliently suspended with shock-absorption in the frame 10 ofthe roller machine by means of buffers 12. The accelerometer 7 isadvantageously mounted substantially straight above the rotational axisof the roller 1. The signal from the accelerometer 7 is fed to signalprocessing circuits 51, in which an electric signal is producedrepresenting the portion oscillating component having half the basefrequency of the oscillation movement of the roller compared to theoscillation components of those frequencies which are equal to or higherthan the base frequency, with which the oscillation movement is excitedby the eccentric mass 3.

The circuits 51 can further in the signal processing also use a signalrepresenting the rotational velocity or the frequency of the rotationalmovement of the eccentric mass 3, this signal being fed from a pulsesensor 33 to the circuits 51 on a wire 52.

The signal from the signal processing circuits 51 are processed by logiccircuits 53 which according to a stored control rule and guided by thesignal produced determine a suitable control signal so that the incomingsignal which represents the oscillation portion having half thefrequency will have a predetermined value. The logic circuits 53 mustthen consider the mechanical limitations of the machine such as amaximally allowed or possible amplitude of the oscillation movement ofthe roller, maximum bearing stresses, etc. The control rule can, for asimple case with only a variation of the amplitude of the oscillationmovement, be such that the excitation by means of the eccentric rotatingmass all the time produces an oscillation amplitude corresponding to thesmaller amplitude value selected among the amplitude producing thedesired oscillation portion having half the frequency and the amplitudewith which the roller machine maximally can be operated.

From the logic circuits 53 signals are transferred to driver circuits55, which when required activate actuating devices 57 for variation ofthe excitation of the eccentric weight 3 of the oscillation movement ofthe roller 1.

In FIGS. 2-3, schematically from the side, two different ways areillustrated for excitation of the vibrations of a rotating roller drum.In FIG. 2 there is, as is indicated in FIG. 1, an eccentrically locatedweight 3 which rotates about the same axis 5 as the roller drum but witha larger velocity than that of the roller. The rotational movement ofthe eccentric body 3 produces a force on the roller drum 1 which has asubstantially constant size and which performs a rotational movement. InFIG. 3 two eccentric weights 3' are arranged which rotate about axeslocated in the same horizontal plane and at a distance from therotational axis of the roller drum 1. When the eccentric weights 3'rotate in opposite directions of each other, forces are obtainedaffecting the roller drum 1 which will be directed substantially in thevertical direction when the relative positions of the eccentric weights3' are such as indicated in the drawing.

In these methods of exciting the roller drum 1 the roller will, as hasalready been indicated, be subjected to a vibrating oscillatingmovement. The size of the oscillation can be influenced, by the methodthat the eccentric body/bodies 3 or 3' respectively e.g. is/are drivenwith larger or smaller rotational velocity, i.e. by varying thefrequency of the excitation. By further changing the size of the mass ofthe eccentric body/bodies 3 and 3' the amplitude of the excitation canbe varied. As a supplement of varying the mass/masses 3 or 3' or insteadit is naturally also possible to change the distance of the mass/massesfrom its/their rotational axis/axes. It can e.g. be accomplished by themethod that the eccentric body or the eccentric bodies each one isdivided into two part masses which can be adjusted in varying angles inrelation to each other and that a first part mass is rigidly attached tothe shaft and that a second part mass can be adjustably turned about theshaft in relation to the first part mass. The common point of inertia ofthe two part masses can in that way be located at different distances oftheir rotational axes.

When the eccentric body rotates, thus a vibration or oscillatingmovement of the roller drum is obtained. This vibration is, when theroller drum 1 is placed on ordinary grounds, not harmonic and thereforeno definite amplitude can be established for the oscillation movement.Instead, as an amplitude of the oscillation movement of the roller for agiven excitation, i.e. with definite excitation conditions resultingfrom the geometry and the mass of the eccentric body, a nominalamplitude can be determined which is the amplitude of the rollervibration or the roller oscillation when the roller is allowed tooscillate freely. More particularly, the nominal amplitude can bedefined as the quotient of the torsional moment of the eccentric body orbodies and the whole mass of the roller. It is independent of theexcitation frequency.

The oscillation movement of the roller cylinder 1 can, as been indicatedabove, be registered or recorded by means of a suitable sensor, whichcan be located on a frame part 9 cushioned in the principal frame 10 ofthe roller machine, in which the roller drum 1 is rotationally mounted,see FIG. 4. The sensor 7 can be designed to measure the acceleration,the oscillation velocity or the displacement but preferably here, in theconventional way, an accelerometer is used. This sensor is then arrangedto sense movements which are performed or takes place substantially inthe vertical direction or generally in some small angle, e.g. smallerthan 30°, in relation to a vertical plane.

In FIG. 5 signals are illustrated which have been registered by anaccelerometer for a vibrating roller and for various excitations of theoscillation of the roller. The top curve shows a case having arelatively low excitation or with a soft ground. The oscillation is notharmonic or sinus shaped but shows overtones due to the asymmetry of theforces influencing the roller. Among other facts the ground can notexert any significant tensile forces but instead more or lesselastically receive compressive forces.

For an increasing excitation or with a stiffer ground and a more elasticground, a certain tendency of double jumps starts to appear, as isvisible in the middle curve of FIG. 5. Every other peak of this curvehas an increased height at the same time as the peaks between thesepeaks have reduced heights. In the top curve the signal has aperiodicity coinciding with the periodicity of the excitation, but inthe middle curve of FIG. 5 instead the periodicity has a frequency orperiodicity which is half the frequency of the excitation. Theoscillatory state, as is illustrated by the middle curve, can still beconsidered as stabile.

When the excitation increases further or the material is still stiffer,the tendencies of the middle curve of FIG. 5 are reinforced and a statehaving distinct pronounced double jumps appears. Every other peak in thelower curve of FIG. 5 increases so that it will have an amplitude of themagnitude of order of the double amplitude compared to the case for alow excitation. Every other peak here vanishes almost completelydepending on the fact that the excitation here makes a stroke when theroller has left the ground, i.e. the excitation has an excitation periodin the air between the blows or jolts against the ground. The proportionof frequency components having half the frequency will in this case bevery high. The dominating excitation in fact takes place having half theoriginal frequency of the original excitation frequency. It will in turnresult in setting the frame of the roller machine (such as 10 in FIG. 4)in a strong oscillation movement. The ground is thus subjected to onlyhalf the number of blows but instead to approximately the double forceamplitude. The compacting effect, however, for this case with very hardblows is ordinarily deteriorated since the ground is subjected to asignificant redisintegration of its earlier compacted state. A furthernegative aspect for this excitation case is that the distances of theindividual blows or jolts against the ground simultaneously will bedouble as high for a given rolling velocity of the roller drum.

Naturally it is desirable that excitation of the oscillation movement ofthe roller is made as strong as possible in order that the compactingand compressing effect of the roller will be as large and as rapid aspossible. Therefore a control condition of the excitation is chosenprincipally as corresponding to the middle curve of FIG. 5. Theexcitation will thus be so large that the resulting roller oscillationwill have a definite proportion of harmonic components having afrequency which is half the excitation frequency. A typical value ofthis proportion of the oscillation having half the frequency can be 5%.In this way still, a stabile travel of the roller machine is obtainedand also a too instable travel of the roller machine is avoided. Toobtain such an operational method a suitable signal processing isrequired, of curves of the type as illustrated in FIG. 5. An electricsignal is obtained, such as has been described above, from the sensor 7and therefrom parameters are produced in the block 51 in FIG. 1, whichin turn are used for the control of parameters influencing theoscillating movement, the size of the oscillatory excitation.

In FIG. 6 the method is illustrated in block diagram shape by which ananalog signal processing can be designed to produce a signal used in thecontrol rule of the logic circuits 53 in FIG. 1 to control a rollermachine in a suitable way. From the accelerometer 7 electric signals areproduced, which are pre-filtered in the filter 11 for removal of thevery highest and very lowest frequencies. After this filtering operationelectric signals are obtained having a curve shape of the kind asillustrated in FIG. 5. These signals are then fed to band-pass filters13 and 15 for a filtering to produce the desired harmonic components.Thus the first band-pass filter 13 has a small pass-band centered aroundthe excitation frequency f_(e), with which the oscillation movement ofthe roller is driven. The second band-pass filter 15 has also a narrowpass-band but it is instead centered around half the excitationfrequency, i.e. around f_(e) /2. After this filtering, from theband-pass filters 13 and 15 principally clean sinus oscillations areobtained which are then rectified in rectifying circuits 17 and 19respectively. From the rectified signal its DC component is extracted inlow-pass filters 21 and 23 respectively.

The DC signals obtained in this way which will then represent theamplitudes of the sinus oscillations as filtered, are divided by eachother in a divisional circuit 25. It produces at its output terminal asignal representing the ratio of the amplitudes of the oscillationmovement, i.e. for half the excitation frequency and for this frequency.The output signal of the division circuit 25 is fed to a controllingdevice in the shape of the control circuits 53, the drive circuits 55and the actuating devices 57, see FIG. 1.

In the case where the excitation frequency is variable, the band-passfilters 13 and 15 must be implemented as filters having controllablefrequencies. These frequencies can then be extracted from thepre-filtered signal itself, which in this case can be fed to apulse-shaping circuit 27, after which an extraction of the basefrequency of the output signal of the circuit 27 is made and a lockingto a definite phase position such as a zero pass or position is made inthe phase-lock circuit 29. The phase-lock circuit 29 can further beconstructed in such a way that it on its output terminal produces apulse train having a frequency n·f_(e) which is proportional to and e.g.is an even multiple of the excitation frequency. This signal isdelivered to the band-pass filter 13, and for the control of the secondband-pass filter in a divisional circuit a signal is generated having afrequency n·f_(e) /2 corresponding to half this frequency. The value ofthe proportionality factor n depends on data of the controllable filtersand can be of the magnitude of order 100.

As an alternative to the extraction of the excitation frequency directlyfrom the pro-filtered signal, a pulse shaper 33 can, as has beenindicated with reference to FIG. 1, be used which in some way senses thebase frequency f_(e) of the excitation. This signal can then directly bedelivered to the phase-lock circuit 29 and then the pulse shaping unit29 is eliminated.

The corresponding signal processing as performed in a digital way isillustrated in the block diagram of FIG. 6. The signal from theaccelerometer 7, which is pre-filtered by the filter 11, is fed to anA/D-converter 35. The A/D-converter is controlled by means of a suitablepulse signal which is obtained from a pulse signal representing thefrequency of the excitation and in this case is shown as obtained from apulse sensor 33, e.g. located to directly sense the rotation of theeccentric body. Advantageously thus the pulse sensor can be arranged onthe bearing plate 9 to sense each passage of some mechanical unevennessor some electric or magnetic inhomogeneity of the shaft of theeccentric. The signal of the accelerometer must be sampled by theA/D-convertor 35 during a time period corresponding to two full turns ofthe rotation of the eccentric body, i.e. two periods of the excitation.The sampling frequency is in an advantageous way selected as a naturalnumber multiplied by the excitation frequency where the natural numberadvantageously can be a power of 2.

The digital signal obtained from the A/D-converter 35 is delivered to asignal processor 37 which performs a mathematic calculation of theFourier-transform of the signal. Then the corresponding signals areobtained, i.e. the size of the DC-component, the amplitudes of theharmonic components having frequencies corresponding to half theexcitation frequency, equal to the excitation frequency, correspondingto three times half the excitation frequency, etc. In particular, herethe amplitudes are obtained for the harmonic components havingfrequencies corresponding to half the excitation frequency and to theexcitation frequency and they are divided by each other to generate anoutput signal of the processor which is used in the control of theroller machine.

For obtaining suitable pulses for the control of the sampling in theA/D-converter 35 the signal from the pulse sensor 33 can as above be fedto a phase-lock circuit 39. In the phase-lock circuit 49 the signalrepresenting the excitation frequency is fed to a phase detector 41. Theoutput signal of the phase detector 41 is delivered to voltage controloscillator 43, the output signal of which is fed back to the phasedetector 41 through a frequency-dividing circuit 45 producing pulseswith a frequency corresponding to the oscillation frequency from theoscillator 43 divided by a natural number n and thus delivers its pulsesignal back to the phase detector 41. The voltage controlled oscillator43 will then produce an output signal of the pulse type having thedesired frequency n·f_(e). The output signal of the oscillator will thenalso have a definite phase position in relation to the signal from thepulse sensor and then in relation to the signal representing theoscillation movement of the roller, which signal, however, the processornot necessarily has to use. The signal of the oscillator 43 is fed tothe A/D-converter 35 for control of the sampling operation thereof.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

I claim:
 1. A method for controlling a body for compacting materialcomprising the steps of:exciting the body to give the body anoscillation movement, the excitation being periodic and having afrequency; sensing said oscillation movement; and controlling theexciting step, so that the resulting oscillating frequency of thevibrating body contains a predetermined proportion of a harmonicoscillation having a frequency corresponding to half the frequency withwhich the body is excited, thereby avoiding undesired oscillationmovement.
 2. The method according to claim 1, wherein the control stepincludes considering only the resulting oscillation movement in a planewhich deviates from a vertical position by at most 30°.
 3. The methodaccording to claim 1, wherein the exciting step includes exciting thebody at different excitation degrees resulting in substantiallydifferent amplitudes in the oscillation movement.
 4. The methodaccording to claim 1, wherein the exciting step, includes exciting thebody at different excitation degrees resulting in substantiallydifferent frequencies in the oscillation movement.
 5. The methodaccording to claim 1, further comprising measuring the oscillationmovement of the vibrating body using a sensor in a direction whichdeviates from the vertical direction by at most 30°.
 6. The methodaccording to claim 5, wherein the measuring step includes harmonicallyanalyzing measured values as a function of the time to determine theamplitude of both a principal oscillation having half the excitationfrequency, and the excitation oscillation having the excitationfrequency, and comparing these amplitudes for use in the controllingstep, so that the amplitude of the oscillation having half theexcitation frequency always corresponds to a predetermined proportion ofthe amplitude of the oscillation having the excitation frequency.
 7. Themethod according to claim 1, further comprising measuring theoscillation movement of the vibrating body by means of an accelerometer.8. The method according to claim 7, wherein the measuring step includesharmonically analyzing measured values as a function of the time todetermine the amplitude of both a principal oscillation having half theexcitation frequency, and the excitation oscillation having theexcitation frequency, and comparing these amplitudes for use in thecontrolling step, so that the amplitude of the oscillation having halfthe excitation frequency always corresponds to a predeterminedproportion of the amplitude of the oscillation having the excitationfrequency.
 9. The method according to claim 1, wherein the exciting stepincludes moving a weight attached to the body.
 10. The method accordingto claim 9, wherein the controlling step includes activating actuatingdevices to vary movement of the weight.
 11. A device for control of abody for compacting a material located underneath the body, the bodybeing arranged to be excited by excitation means to give the body anoscillation movement, the excitation being periodic and having afrequency, comprising a controller adjusting the excitation means inaccordance with the oscillation movement so that the resultingoscillating movement of the vibrating body contains a predeterminedproportion of a harmonic oscillation having a frequency corresponding tohalf the frequency with which the vibrating body is excited, therebyavoiding undesired oscillation movement.
 12. The device according toclaim 11 wherein the controller is arranged to only consider theresulting oscillation movement of the body in a plane which deviatesfrom the vertical position by at most 30°.
 13. The device according toclaim 11, further comprising a sensor for measuring the oscillationmovement of the vibrating body.
 14. The device according to claim 13,wherein further comprising means for mounting the sensor for adetermination of the acceleration of the body in a direction whichdeviates from a vertical direction by at most 30°.
 15. The deviceaccording to claim 13, further comprising means for attaching the sensorto the body or to a part in which the body is rotatably mounted.
 16. Thedevice according to claim 13, wherein the sensor is an accelerometer.17. The device according to claim 13, further comprising calculationmeans for analysing harmonically the registered values of theoscillation movement as a function of time in order to determine theamplitude of both an oscillation having half the excitation frequencyand the oscillation having the excitation frequency, the controllerbeing arranged to compare these amplitudes in the control and theadjustment of the excitation means, so that the amplitude of theoscillation having half the excitation frequency always corresponds to apredetermined proportion of the amplitude of the oscillation having theexcitation frequency.
 18. The device according to claim 11, wherein thebody is excited by moving a weight attached thereto and the controllervaries movement of the weight.
 19. The device according to claim 18,wherein the controller varies at least one of rotational velocity of theweight, amplitude of the weight and the distance of the weight from itsrotational axis.